The cryogenic rectification of air to produce oxygen, nitrogen and/or argon is a well established industrial process. Typically the feed air is separated into nitrogen and oxygen in a double column system wherein nitrogen-rich top vapor from a higher pressure column is used to reboil oxygen-rich bottom liquid in a lower pressure column. Fluid from the lower pressure column is passed into an argon side arm column for the production of argon.
A significant thermodynamic irreversibility present in a double column cryogenic air separation system with a side arm column attached to the lower pressure column for the production of argon is the large temperature difference between the boiling kettle liquid and condensing argon in the argon column top condenser. This temperature difference can be greater than 5 degrees C. compared with a temperature difference of less than 1.5 degrees C. which is common for the main condenser linking the higher and lower pressure columns. The magnitude of the lost work owing to the argon condenser irreversibility is large in comparison to the gain in efficiency from other improvements to modern air separation systems. For this reason, a modified cryogenic air separation system wherein the size of this irreversibility is reduced would clearly be useful.
Accordingly, it is an object of this invention to provide an improved cryogenic rectification system wherein the thermodynamic irreversibility between the argon column top condenser and the lower pressure column is reduced.